A pump to be used in a conventional heat pump apparatus employing water as a refrigerant includes a stator part, a rotor part, a pump part, and a shaft. The shaft is fixed, and the rotor part freely rotates around the shaft. The stator part includes an iron core formed of stacked electromagnetic steel sheets, a winding that is wound around a slot of the iron core via an insulator (insulating material), a circuit board connected with a lead line, and an approximately pot-shaped lower casing in a hollow cylindrical shape having a bottom part. The circuit board is positioned near the stator part at a side opposite from the pump part. The rotor part is housed in a hollow cylindrical interior of the approximately pot-shaped lower casing. At an approximately center portion of the bottom part of the lower casing, an axial hole is formed for fitting the shaft therein. The shaft is fitted into the axial hole in a non-rotating manner. To achieve this, the shaft to be fitted into the axial hole has a notched portion in its circular shape. The shaft is also shaped in the same fashion at another end thereof facing the pump part. The axial hole is also shaped in a nearly identical fashion to the shaft, with a diameter slightly larger than that of the shaft (as disclosed, for example, in Patent Documents 1 and 2).